This invention relates to driver circuits for automatic digital testing apparatus.
One known form of digital test apparatus comprises a plurality of driver circuits which, in use, are connected to respective terminals of the equipment under test, so as to permit test signals to be injected into the equipment. Some of the terminals may alternatively be used to receive response signals from the equipment under test, for comparison with the expected responses.
The equipment under test may be of a variety of different types. For example it may comprise ECL (emitter-coupled logic) or TTL (transistor-transistor logic) circuits. Different types of logic circuit generally use different voltage levels to represent the binary digits "0" and "1". Moreover, different types of logic generally also require different matching networks to be connected to terminals which receive response signals from the equipment under test.
In the past, these requirements have meant that different driver circuits have had to be provided for different types of logic. This is very expensive. The object of the present invention is therefore to provide a driver circuit which is capable of being used with more than one type of equipment.